In connection with hot melt adhesive dispensing systems, failures can generally occur within two different categories, that is, mechanical failures due to wear, or electrical failures due to electrical malfunctions. More particularly, in connection with the different types of electrical failures that can be experienced, electrical failures can occur, for example, either within the heater circuit which is used to maintain the hot melt adhesive material, which is flowing through the hot melt adhesive hose assembly, at a predetermined temperature level, or within the temperature sensor which is operatively or thermally associated with the hot melt adhesive hose assembly in order to effectively detect the temperature level of the hot melt adhesive material, which is flowing through the hot melt adhesive hose assembly, and to appropriately control the heater circuit so as to effectively ensure that the desired temperature level of the hot melt adhesive material, which is flowing through the hot melt adhesive hose assembly, is in fact maintained. Maintenance of the proper or desired temperature level of the hot melt adhesive material is of course critical in order to ensure that the hot melt adhesive material will be properly dispensed, and provide the desired adhesive properties, once the hot melt adhesive material is in fact deposited onto a particular substrate. In either case, that is, whether a failure is experienced in connection with the heater circuit, or in connection with the temperature sensor, such failures typically cause the hot melt adhesive dispensing production line to be shut down for extended periods of time, in order to implement the repair or replacement of the failed components, whereby valuable production time is lost.
In addition, the temperature zones defined within, or encountered in connection with, standard hot melt adhesive application equipment are effectively organized in pairs comprising the hot melt adhesive supply hose and the hot melt adhesive applicator head. If a particular one of the hot melt adhesive applicator heads is relatively large, then it usually comprises a plurality of cartridge heaters or heater circuits, connected in parallel, but only a single temperature sensor which is usually located at a relatively central region of the applicator head so as to sense, in effect, an average or median temperature reading for the applicator head. Accordingly, based upon such an average or median temperature reading sensed by means of the single temperature sensor, suitable electrical power is sent to each cartridge heater or heater circuit by means of the adhesive supply unit (ASU) temperature controller. However, due to tolerances and unbalanced heat distribution factors or characteristics, the actual temperatures at the different locations can differ significantly which can, of course, ultimately lead to performance problems comprising, for example, improperly heated hot melt adhesive material which will, of course, in turn, lead to improperly or incompletely bonded products.
Ideally, therefore, it would be desirable to distribute and adjust the electrical power being supplied from the adhesive supply unit (ASU) temperature controller to each one of the plurality of cartridge heaters or heater circuits in such a manner that all of the cartridge heaters or heater circuits would maintain the same predetermined or set temperature level. One possible solution to this dilemma would be to install additional temperature sensors within the applicator head and let the adhesive supply unit (ASU) temperature controller control each zone independently with a common temperature set point. However, this solution has several operational problems, disadvantages, and drawbacks. For example, each cartridge heater or heater circuit, and its respective temperature sensor, would require its own temperature zone upon the adhesive supply unit (ASU) temperature controller, however the number of zones available upon the adhesive supply unit (ASU) temperature controller are limited. Secondly, each temperature zone would require a separate cable and connector, which would entail or require an extensive amount of electrical connections, routing, and the like. Thirdly, even though the temperature set point for all of the cartridge heaters or heater circuits, and their respective temperature sensors, would be the same, each temperature zone would have to be individually programmed.
Continuing still further, and in accordance with a potentially alternative mode of operation, it is desirable to effectively eliminate the need for the plurality of temperature sensors so as to render the hot melt adhesive application equipment more economical to produce. It is known that each heater circuit or wire has an inherent or predetermined electrical temperature coefficient, and that there is also a predetermined or known relationship between the temperature of a wire and its electrical resistance. Accordingly, if the resistance of the heater circuit or wire can be determined, then the temperature of the heater circuit or wire can be determined whereby the temperature sensors could effectively be eliminated.
A need therefore exists in the art for a new and improved redundant control circuit, for use in conjunction with a hot melt adhesive hose assembly, wherein redundant electrical components could effectively be incorporated such that if a failure occurs within a particular electrical component, the failed electrical component could effectively be removed from its operative or functional disposition within the electrical circuitry, and the other electrical component could effectively be operatively or functionally incorporated into the electrical circuitry. In this manner, the hot melt adhesive dispensing production line would not need to be shut down for extended periods of time, in order to implement the replacement of the failed hot melt adhesive hose assembly, whereby valuable production time would not be lost. In addition, a need also exists in the art for a new and improved electronic control circuit, for use in connection with hot melt adhesive application equipment, and in particular, in conjunction with a relatively large application head comprising a plurality of cartridge heaters or heater circuits, wherein a plurality of temperature sensors may respectively be used in conjunction with the plurality of cartridge heaters or heater circuits whereby the number of zones upon the adhesive supply unit (ASU) temperature controller need not be increased and yet all of the plurality of cartridge heaters or heater circuits can be individually and independently controlled. Still further, a need exists in the art for a new and improved electronic control circuit, for use in connection with hot melt adhesive application equipment, wherein the use of temperature sensors can effectively be eliminated, and yet the temperature of each one of a plurality of cartridge heaters or heater circuits can nevertheless be determined such that the adhesive supply unit (ASU) temperature controller can individually and independently control the cartridge heaters or heater circuits.